Hi, According to your description the possibility of pregnancy is very less, as: -You have undergone tubal ligation.-And as all your pregnancy tests including the blood test gave negative results. Sometimes excessive and continuous thinking regarding the pregnancy can lead to pregnancy like symptoms which is called as spurious pregnancy.Irregularity in menstrual cycles can occur due to many causes like psychological factors, hormonal, systemic, etc. By undergoing ultrasound and by direct visualization of empty uterus on screen, you can come out of the thoughts of pregnancy.If the irregularity in periods persist, by undergoing other investigations like hemoglobin, blood sugar levels, thyroid profile, etc. the possible cause of irregularity can be identified and treatment can be taken accordingly. Hope I have answered your query. Let me know if I can assist you further. Take care Regards, Dr. Sree Gouri SR